Treatment outcomes cannot be predicted without knowing principles of a normal functioning state, or of adaptation to new functional states. The purpose of this research project is to evaluate the biomechanical differences between the (I) minimally and (2) severely resorbed edentulous mandibles and the (3) dentulous mandible. Regional bone quality and quantity, measured by material properties and architectural differences, directly impacts the biomechanics of the whole mandible. Material property testing is carried out using an ultrasonic pulse transmission technique, and moduli (including Young's and shear modulus) are derived from the principles of linear elastic wave theory. Data are examined by region, and variations correspond to functional changes in response to tooth loss. The construction, solution, and validation of two finite element models of the edentulous mandible are analyzed and compared to a dentate mandibular model. The mandibles are imaged, and the geometry is digitized and imported for three dimensional computer reconstruction and finite element analysis. Varied simulated patterns of loading are examined. The resulting deformations and internal stresses are evaluated for similarities and/or differences with published dentulous models. Regional maximum load capabilities and the changes in these capabilities with dental and bone loss are also examined. BiomechanicaI evaluation determines the sources of geometric, density, and material property differences between edentulous and dentulous mandibles.